MPLS Working Group G. Mirsky
Internet-Draft S. Ruffini
Intended status: Standards Track E. Gray
Expires: November 3, 2015 Ericsson
J. Drake
Juniper Networks
S. Bryant
Cisco Systems
A. Vainshtein
ECI Telecom
May 2, 2015
Residence Time Measurement in MPLS network
draft-mirsky-mpls-residence-time-06
Abstract
This document specifies G-ACh based Residence Time Measurement and
how it can be used by time synchronization protocols being
transported over MPLS domain.
Residence time is the variable part of propagation delay of timing
and synchronization messages and knowing what this delay is for each
message allows for a more accurate determination of the delay to be
taken into account in applying the value included in a PTP event
message.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 3, 2015.
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Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions used in this document . . . . . . . . . . . . 3
1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3
1.1.2. Requirements Language . . . . . . . . . . . . . . . . 4
2. Residence Time Measurement . . . . . . . . . . . . . . . . . 4
3. G-ACh for Residence Time Measurement . . . . . . . . . . . . 4
3.1. PTP Packet Sub-TLV . . . . . . . . . . . . . . . . . . . 6
4. Control Plane Theory of Operation . . . . . . . . . . . . . . 7
4.1. RTM Capability . . . . . . . . . . . . . . . . . . . . . 7
4.2. RTM Capability Sub-TLV . . . . . . . . . . . . . . . . . 8
4.3. RTM Capability Advertisement in OSPFv2 . . . . . . . . . 9
4.4. RTM Capability Advertisement in OSPFv3 . . . . . . . . . 9
4.5. RTM Capability Advertisement in IS-IS . . . . . . . . . . 10
4.6. RSVP-TE Control Plane Operation to Support RTM . . . . . 10
4.7. RTM_SET Object . . . . . . . . . . . . . . . . . . . . . 11
4.7.1. RSO Sub-objects . . . . . . . . . . . . . . . . . . . 12
5. Data Plane Theory of Operation . . . . . . . . . . . . . . . 14
6. Applicable PTP Scenarios . . . . . . . . . . . . . . . . . . 15
7. One-step Clock and Two-step Clock Modes . . . . . . . . . . . 15
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
8.1. New RTM G-ACh . . . . . . . . . . . . . . . . . . . . . . 17
8.2. New RTM TLV Registry . . . . . . . . . . . . . . . . . . 18
8.3. New RTM Sub-TLV Registry . . . . . . . . . . . . . . . . 18
8.4. RTM Capability sub-TLV . . . . . . . . . . . . . . . . . 19
8.5. IS-IS RTM Application ID . . . . . . . . . . . . . . . . 19
8.6. RTM_SET Object RSVP Class Number, Class Type and Sub-
object Types . . . . . . . . . . . . . . . . . . . . . . 19
9. Security Considerations . . . . . . . . . . . . . . . . . . . 20
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 21
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
11.1. Normative References . . . . . . . . . . . . . . . . . . 21
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11.2. Informative References . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction
Time synchronization protocols, Network Time Protocol version 4
(NTPv4) [RFC5905] and Precision Time Protocol (PTP) Version 2
[IEEE.1588.2008] can be used to synchronize clocks across network
domain. Measurement of the time a PTP event message spends
traversing a node (using precise times of receipt at an ingress
interface and transmission at an egress interface), called Residence
Time, can be used to improve the accuracy of clock synchronization.
This document defines new Generalized Associated Channel (G-ACh) that
can be used in Multi-Protocol Label Switching (MPLS) network to
measure Residence Time over Label Switched Path (LSP). Mechanisms
for transport of time synchronization protocol packets over MPLS are
out of scope in this document.
1.1. Conventions used in this document
1.1.1. Terminology
MPLS: Multi-Protocol Label Switching
ACH: Associated Channel
TTL: Time-to-Live
G-ACh: Generic Associated Channel
GAL: Generic Associated Channel Label
NTP: Network Time Protocol
ppm: parts per million
PTP: Precision Time Protocol
LSP: Label Switched Path
LSR: Label Switching Router
OAM: Operations, Administration, and Maintenance
RRO: Record Route Object
RSO: RTM Set Object
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RTM: Residence Time Measurement
IGP: Internal Gateway Protocol
1.1.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
2. Residence Time Measurement
Packet Loss and Delay Measurement for MPLS Networks [RFC6374] can be
used to measure one-way or two-way end-to-end propagation delay over
LSP or PW. But these metrics are insufficient for use in some
applications, for example, time synchronization across a network as
defined in the Precision Time Protocol (PTP). PTPv2 [IEEE.1588.2008]
uses "residence time", the time it takes for a PTPv2 event packet to
transit a node. Residence times are accumulated in the
correctionField of the PTP event messages, as defined in
[IEEE.1588.2008], or of the associated follow-up messages (or
Delay_Resp message associated with the Delay_Req message) in case of
two-step clocks (detailed discussion in Section 7). The residence
time values are specific to each output PTP port and message.
IEEE 1588 uses this residence time to correct the propagated time,
effectively making these nodes transparent.
This document proposes mechanism to accumulate packet residence time
from all LSRs that support the mechanism across a particular LSP.
The values accumulated in scratchpad fields of MPLS RTM messages can
be used by the last RTM-capable LSR on an LSP to update the
correctionField of the corresponding PTP event packet prior to
performing the usual PTP processing.
3. G-ACh for Residence Time Measurement
RFC 5586 [RFC5586] and RFC 6423 [RFC6423] extended applicability of
PW Associated Channel (ACH) [RFC5085] to LSPs. G-ACh provides a
mechanism to transport OAM and other control messages. Processing by
arbitrary transit LSRs can be triggered through controlled use of the
Time-to-Live (TTL) value. In a way that is analogous to PTP
operations, the packet residence time can be handled by the RTM
capable node either as "one-step clock" or as a "two-step clock".
The packet format for Residence Time Measurement (RTM) is presented
in Figure 1
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|Version| Reserved | RTM Channel |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Scratch Pad |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: RTM G-ACh packet format for Residence Time Measurement
o First four octets are defined as G-ACh Header in [RFC5586]
o The Version field is set to 0, as defined in RFC 4385 [RFC4385].
o The Reserved field MUST be set to 0 on transmit and ignored on
receipt.
o The RTM G-ACh field, value to be allocated by IANA, identifies the
packet as such.
o The Scratch Pad field is 8 octets in length. The first RTM-
capable LSR MUST initialize the Scratch Pad field, it SHOULD set
it to zero value. The Scratch Pad is used to accumulate the
residence time spent in each RTM capable LSR transited by the
packet on its path from ingress LSR to egress LSR. Its format is
IEEE double precision and its units are nanoseconds. Note:
depending on one-step or two-step operation (Section 7), the
residence time might be related to the same packet carried in the
Value field or to a packet carried in a different RTM packet.
o The Type field identifies the type of Value that the TLV carries.
IANA will be asked to create a sub-registry in Generic Associated
Channel (G-ACh) Parameters Registry called "MPLS RTM TLV
Registry".
o The Length field contains the number of octets of the Value field.
o The optional Value field may be used to carry a packet of a given
time synchronization protocol. If packet data is carried in the
RTM message, then this is identified by Type accordingly. The
data MAY be NTP [RFC5905] or PTP [IEEE.1588.2008]. It is
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important to note that the packet may be authenticated or
encrypted and carried over MPLS LSP edge to edge unchanged while
residence time being accumulated in the Scratch Pad field. Sub-
TLVs MAY be included in the Value field.
o The TLV MUST be included in the RTM message, even if the length of
the Value field is zero.
3.1. PTP Packet Sub-TLV
Figure 2 presents format of a PTP sub-TLV that MUST be precede every
PTP packet carried in RTM TLV.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |PTPType|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Port ID |
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Sequence ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: PTP Sub-TLV format
where Flags field has format
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Flags field format of PTP Packet Sub-TLV
o The Type field identifies PTP sub-TLV defined in the Table 19
Values of messageType field in [IEEE.1588.2008].
o The Length field of the PTP sub-TLV contains the number of octets
of the Value field and MUST be 20.
o The Flags field currently defines one bit, the S-bit, that defines
whether or not the current message has been processed by a 2-step
node, where the flag is cleared if the message has been handled
exclusively by 1-step nodes and there is no follow-up message, and
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set if there has been at least one 2-step node and a follow-up
message is forthcoming.
o The PTPType indicates the type of PTP packet carried in the TLV.
PTPType is the messageType field of the PTPv2 packet whose values
are defined in the Table 19 [IEEE.1588.2008].
o The 10 octets long Port ID field contains the identity of the
source port.
o The Sequence ID is the sequence ID of the PTP message carried in
the Value field of the message.
4. Control Plane Theory of Operation
The operation of RTM depends upon TTL expiry to deliver an RTM packet
from one RTM capable interface to the next along the path from
ingress LSR to egress LSR. This means that an LSR with RTM capable
interfaces MUST be able to compute a TTL which will cause the expiry
of an RTM packet at the next LSR with RTM capable interfaces.
However, because of Equal Cost Multipath, labels distributed by LDP
do not necessarily instantiate a single path between a given ingress/
egress LSR pair but rather MAY create a graph in which different
flows will take different paths through this network. This means one
doesn't necessarily know the path that RTM packets will take or even
if they all take the same path. In an environment in which not all
interfaces in an IGP domain support RTM, it is effectively impossible
to use TTL expiry to deliver RTM packets. Hence RTM cannot be used
for LSPs instantiated using LDP, if multi-pathing is in use and not
all LSRs are RTM-capable. In the special but important case of
environment in which all interfaces in an IGP domain support RTM,
setting the TTL to 1 will always cause the expiry of an RTM packet on
the next RTM capable downstream LSR and hence in such an environment,
RTM can be used for LSPs instantiated using LDP.
Also, if it is possible and desirable, multi-path forwarding may be
disabled,at least for LSPs used for RTM.
Generally speaking, RTM is more useful for an LSP instantiated using
RSVP-TE [RFC3209] because the LSP's path can be determined.
4.1. RTM Capability
Note that RTM capability of a node is with respect to the pair of
interfaces that will be used to forward an RTM packet. In general,
the ingress interface of this pair must be able to capture the
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arrival time of the packet and encode it in some way such that this
information will be available to the egress interface.
The supported modes (1-step verses 2-step) of any pair of interfaces
is then determined by the capability of the egress interface. In
both cases, the egress interface implementation MUST be able to
determine the precise departure time of the same packet and determine
from this, and the arrival time information from the corresponding
ingress interface, the difference representing the residence time for
the packet.
An interface with the ability to do this and update the associated
ScratchPad in real-time (i.e. while the packet is being forwarded) is
said to be 1-step capable.
Hence while both ingress and egress interfaces are required to
support RTM, for the pair to be RTM-capable, it is the egress
interface that determines whether or not the node is 1-step or 2-step
capable with respect to the interface-pair.
The RTM capability used in the sub-TLV shown in Figure 4 is thus
associated with the egress port of the node making the advertisement,
while the ability of any pair of interfaces that includes this egress
interface to support any mode of RTM depends on the ability of that
interface to record packet arrival time in some way that can be
conveyed to and used by that egress interface.
When an LSR uses an IGP to carry the RTM capability sub-TLV, the sub-
TLV MUST reflect the RTM capability (1-step or 2-step) associated
with egress interfaces and MUST NOT propagate this sub-TLV in IGP
LSAs sent from an interface that does not support the same capability
for RTM messages it receives.
4.2. RTM Capability Sub-TLV
The format for the RTM Capabilities sub-TLV is presented in Figure 4
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type(TBA5) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RTM | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: RTM Capability sub-TLV
o Type value will be assigned by IANA from appropriate registries.
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o Length MUST be set to 4.
o RTM (capability) - is a three-bit long bit-map field with values
defined as follows:
* 0b001 - one-step RTM supported;
* 0b010 - two-step RTM supported;
* 0b100 - reserved.
o Reserved field must be set to all zeroes on transmit and ignored
on receipt.
[RFC4202] explains that the Interface Switching Capability Descriptor
describes switching capability of an interface. For bi-directional
links, the switching capabilities of an interface are defined to be
the same in either direction. I.e., for data entering the node
through that interface and for data leaving the node through that
interface". That principle SHOULD be applied when a node advertises
RTM Capability.
A node that supports RTM MUST be able to act in two-step mode and MAY
also support one-step RTM mode. Detailed discussion of one-step and
two-step RTM modes in Section 7.
4.3. RTM Capability Advertisement in OSPFv2
The capability to support RTM on a particular link advertised in the
OSPFv2 Extended Link Opaque LSA [I-D.ietf-ospf-prefix-link-attr] as
RTM Capability sub-TLV, presented in Figure 4, of the OSPFv2 Extended
Link TLV.
Type value will be assigned by IANA from the OSPF Extended Link TLV
Sub-TLVs registry that will be created per
[I-D.ietf-ospf-prefix-link-attr] request.
4.4. RTM Capability Advertisement in OSPFv3
The capability to support RTM on a particular link in OSPFv3 can be
advertised by including an RTM Capability sub-TLV defined in
Section 4.3 in the following TLVs defined in
[I-D.ietf-ospf-ospfv3-lsa-extend] Intra-Area-Prefix TLV, IPv6 Link-
Local Address TLV, or IPv4 Link-Local Address TLV when these are
included in E-Link-LSA.
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4.5. RTM Capability Advertisement in IS-IS
The RTM capability logically belongs to a group of parameters
characterized as "generic information not directly related to the
operation of the IS-IS protocol" [RFC6823]. Hence the capability to
process RTM messages can be advertised by including RTM Capability
sub-TLV in GENINFO TLV [RFC6823].
With respect to the Flags field of the GENINFO TLV:
o The S bit MUST be cleared to prevent the RTM Capability sub-TLV
from leaking between levels.
o The D bit of the Flags field MUST be cleared as required by
[RFC6823].
o The I bit and the V bit MUST be set accordingly depending on
whether RTM capability being advertised for IPv4 or IPv6 interface
of the node.
Application ID (TBA6) will be assigned from the Application
Identifiers for TLV 251 IANA registry. The RTM Capability sub-TLV,
presented in Figure 4, MUST be included in GENINFO TLV in Application
Specific Information.
4.6. RSVP-TE Control Plane Operation to Support RTM
Though RTM capability is per interface throughout this document we
will refer to an LSR as RTM capable LSR when:
o ingress LSR's LSP interface is RTM capable;
o transit LSR's ingress and egress interfaces for the given LSP are
RTM capable;
o egress LSR's egress interface is RTM capable.
An ingress LSR that is configured to perform RTM along a path through
an MPLS network to an egress LSR verifies that the selected egress
LSR has an interface that supports RTM via the egress LSR's
advertisement of the RTM Capability sub-TLV. In the Path message
that the ingress LSR uses to instantiate the LSP to that egress LSR
it places initialized Record Route Object (RRO) [RFC3209] and RTM Set
Object (RSO) [Section 4.7], which tell the egress LSR that RTM is
requested for this LSP.
In the Resv message that the egress LSR sends in response to the
received Path message, it includes initialized RRO and RSO. The RSO
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contains an ordered list, from egress LSR to ingress LSR, of the RTM
capable LSRs along the LSP's path. Each such LSR will use the ID of
the first LSR in the RSO in conjunction with the RRO to compute the
hop count to its downstream LSR with reachable RTM capable interface.
It will also insert its ID at the beginning of the RTM Set Object
before forwarding the Resv upstream.
After the ingress LSR receives the Resv, it MAY begin sending RTM
packets to the first RTM capable LSR on the LSP's path. Each RTM
packet has its Scratch Pad field initialized and its TTL set to
expire on that first subsequent RTM capable LSR.
It should be noted that RTM can also be used for LSPs instantiated
using [RFC3209] in an environment in which all interfaces in an IGP
support RTM. In this case the RSO MAY be omitted.
4.7. RTM_SET Object
RTM capable interfaces can be recorded via RTM_SET object (RSO). The
RTM Set Class is TBA7. This document defines one C_Type, Type TBA8
RTM Set. The RTM_SET object format presented in Figure 5
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Sub-objects ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: RTM Set object format
The contents of a RTM_SET object are a series of variable-length data
items called sub-objects. The sub-objects are defined in
Section 4.7.1 below.
The RSO can be present in both RSVP Path and Resv messages. If a
Path message contains multiple RSOs, only the first RSO is
meaningful. Subsequent RSOs SHOULD be ignored and SHOULD NOT be
propagated. Similarly, if in a Resv message multiple RSOs are
encountered following a FILTER_SPEC before another FILTER_SPEC is
encountered, only the first RSO is meaningful. Subsequent RSOs
SHOULD be ignored and SHOULD NOT be propagated.
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4.7.1. RSO Sub-objects
The RTM Set object contains an ordered list, from egress LSR to
ingress LSR, of the RTM capable LSRs along the LSP's path.
The contents of a RTM_SET object are a series of variable-length data
items called sub-objects. Each sub-object has its own Length field.
The length contains the total length of the sub-object in bytes,
including the Type and Length fields. The length MUST always be a
multiple of 4, and at least 8 (smallest IPv4 sub-object).
Sub-objects are organized as a last-in-first-out stack. The first
-out sub-object relative to the beginning of RSO is considered the
top. The last-out sub-object is considered the bottom. When a new
sub-object is added, it is always added to the top.
Three kinds of sub-objects for RSO are currently defined.
4.7.1.1. IPv4 Sub-object
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: IPv4 sub-object format
Type
0x01 IPv4 address
Length
The Length contains the total length of the sub-object in bytes,
including the Type and Length fields. The Length is always 8.
IPv4 address
A 32-bit unicast host address.
Flags
TBD
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4.7.1.2. IPv6 Sub-object
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: IPv6 sub-object format
Type
0x02 IPv6 address
Length
The Length contains the total length of the sub-object in bytes,
including the Type and Length fields. The Length is always 20.
IPv6 address
A 128-bit unicast host address.
Flags
TBD
4.7.1.3. Unnumbered Interface Sub-object
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: IPv4 sub-object format
Type
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0x03 Unnumbered interface
Length
The Length contains the total length of the sub-object in bytes,
including the Type and Length fields. The Length is always 12.
Router ID
The Router ID interpreted as discussed in the Section 2 of RFC
3447 [RFC3477].
Interface ID
The identifier assigned to the link by the LSR specified by the
Router ID.
Flags
TBD
5. Data Plane Theory of Operation
After instantiating an LSP for a path using RSVP-TE [RFC3209] as
described in Section 4.6 or as described in the second paragraph of
Section 4 and in Section 4.6, ingress LSR MAY begin sending RTM
packets to the first downstream RTM capable LSR on that path. Each
RTM packet has its Scratch Pad field initialized and its TTL set to
expire on the next downstream RTM-capable LSR. Each RTM-capable LSR
on the explicit path receives an RTM packet and records the time at
which it receives that packet at its ingress interface as well as the
time at which it transmits that packet from its egress interface;
this should be done as close to the physical layer as possible to
ensure precise accuracy in time determination. The RTM-capable LSR
determines the difference between those two times; for 1-step
operation, this difference is determined just prior to or while
sending the packet, and the RTM-capable egress interface adds it to
the value in the Scratch Pad field of the message in progress. Note,
for the purpose of calculating a residence time, a common free
running clock synchronizing all the involved interfaces may be
sufficient, as, for example, 4.6 ppm accuracy leads to 4.6 nanosecond
error for residence time on the order of 1 millisecond.
For 2-step operation, the difference between packet arrival time (at
an ingress interface) and subsequent departure time (from an egress
interface) is determined at some later time prior to sending a
subsequent follow-up message, so that this value can be used to
update the correctionField in the follow-up message.
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See Section 7 for further details on the difference between 1-step
and 2-step operation.
The last RTM-capable LSR on the LSP MAY then use the value in the
Scratch Pad field to perform time correction, if there is no follow-
up message. For example, the egress LSR may be a PTP Boundary Clock
synchronized to a Master Clock and will use the value in the Scratch
Pad Field to update PTP's correctionField.
6. Applicable PTP Scenarios
The proposed approach can be directly integrated in a PTP network
based on the IEEE 1588 delay reqest-response mechanism. The RTM
capable LSR nodes act as end-to-end transparent clocks, and typically
boundary clocks, at the edges of the MPLS network, use the value in
the Scratch Pad field to update the correctionField of the
corresponding PTP event packet prior to performing the usual PTP
processing.
7. One-step Clock and Two-step Clock Modes
One-step mode refers to the mode of operation where an egress
interface updates the correctionField value of an original event
message. Two-step mode refers to the mode of operation where this
update is made in a subsequent follow-up message.
Processing of the follow-up message, if present, requires the
downstream end-point to wait for the arrival of the follow-up message
in order to combine correctionField values from both the original
(event) message and the subsequent (follow-up) message. In a similar
fashion, each 2-step node needs to wait for the related follow-up
message, if there is one, in order to update that follow-up message
(as opposed to creating a new one. Hence the first node that uses
2-step mode MUST do two things:
1. Mark the original event message to indicate that a follow-up
message will be forthcoming (this is necessary in order to
Let any subsequent 2-step node know that there is already a
follow-up message, and
Let the end-point know to wait for a follow-up message;
2. Create a follow-up message in which to put the RTM determined as
an initial correctionField value.
IEEE 1588v2 [IEEE.1588.2008] defines this behaviour for PTP messages.
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Thus, for example, with reference to the PTP protocol, the PTPType
field identifies whether the message is a Sync message, Follow_up
message, Delay_Req message, or Delay_Resp message. The 10 octet long
Port ID field contains the identity of the source port, that is, the
specific PTP port of the boundary clock connected to the MPLS
network. The Sequence ID is the sequence ID of the PTP message
carried in the Value field of the message.
PTP messages also include a bit that indicates whether or not a
follow-up message will be coming. This bit, once it is set by a
2-step mode device, MUST stay set accordingly until the original and
follow-up messages are combined by an end-point (such as a Boundary
Clock).
Thus, an RTM packet, containing residence time information relating
to an earlier packet, also contains information identifying that
earlier packet.
For compatibility with PTP, RTM (when used for PTP packets) must
behave in a similar fashion. To do this, a 2-step RTM capable egress
interface will need to examine the S-bit in the Flags field of the
PTP sub-TLV (for RTM messages that indicate they are for PTP) and -
if it is clear (set to zero), it MUST set it and create a follow-up
PTP Type RTM message. If the S bit is already set, then the RTM
capable node MUST wait for the RTM message with the PTP type of
follow-up and matching originator and sequence number to make the
corresponding residence time update to the Scratch Pad field.
In practice an RTM operating according to two-step clock behaves like
a two-steps transparent clock.
A 1-step capable RTM node MAY elect to operate in either 1-step mode
(by making an update to the Scratch Pad field of the RTM message
containing the PTP even message), or in 2-step mode (by making an
update to the scratch pad of a follow-up message when its presence is
indicated), but MUST NOT do both.
Two main subcases can be identified for an RTM node operating as a
two-step clock:
A) If any of the previous RTM capable node or the previous PTP clock
(e.g. the BC connected to the first LSR), is a two-step clock, the
residence time is added to the RTM packet that has been created to
include the associated PTP packet (i.e. follow-up message in the
downstream direction), if the local RTM-capable LSR is also operating
as a two-step clock. This RTM packet carries the related accumulated
residence time and the appropriate values of the Sequence Id and Port
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Id (the same identifiers carried in the packet processed) and the
Two-step Flag set to 1.
Note that the fact that an upstream RTM-capable node operating in the
two-step mode has created a follow-up message does not require any
subsequent RTM capable LSR to also operate in the 2-step mode, as
long as that RTM-capable LSR forwards the follow-up message on the
same LSP on which it forwards the corresponding previous message.
A one-step capable RTM node MAY elect to update the RTM follow-up
message as if it were operating in two-step mode, however, it MUST
NOT update both messages.
A PTP event packet (sync) is carried in the RTM packet in order for
an RTM node to identify that residence time measurement must be
performed on that specific packet.
To handle the residence time of the Delay request message on the
upstream direction, an RTM packet must be created to carry the
residence time on the associated downstream Delay Resp message.
The last RTM node of the MPLS network in addition to update the
correctionField of the associated PTP packet, must also properly
handle the two-step flag of the PTP packets.
B) When the PTP network connected to the MPLS and RTM node, operates
in one-step clock mode, the associated RTM packet must be created by
the RTM node itself. The associated RTM packet including the PTP
event packet needs now to indicate that a follow up message will be
coming.
The last RTM node of the LSP, modeif it receives an RTM message with
a PTP payload indicating a follow-up message will be forthcoming,
must generate a follow-up message and properly set the two-step flag
of the PTP packets.
8. IANA Considerations
8.1. New RTM G-ACh
IANA is requested to reserve a new G-ACh as follows:
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+-------+----------------------------+---------------+
| Value | Description | Reference |
+-------+----------------------------+---------------+
| TBA1 | Residence Time Measurement | This document |
+-------+----------------------------+---------------+
Table 1: New Residence Time Measurement
8.2. New RTM TLV Registry
IANA is requested to create sub-registry in Generic Associated
Channel (G-ACh) Parameters Registry called "MPLS RTM TLV Registry".
All code points in the range 0 through 127 in this registry shall be
allocated according to the "IETF Review" procedure as specified in
[RFC5226] . Remaining code points are allocated according to the
table below. This document defines the following new values RTM TLV
type s:
+-----------+-------------+-------------------------+
| Value | Description | Reference |
+-----------+-------------+-------------------------+
| 0 | Reserved | This document |
| 1 | No payload | This document |
| 2 | PTPv2 | This document |
| 3 | NTP | This document |
| 4-127 | Reserved | IETF Consensus |
| 128 - 191 | Reserved | First Come First Served |
| 192 - 255 | Reserved | Private Use |
+-----------+-------------+-------------------------+
Table 2: RTM TLV Type
8.3. New RTM Sub-TLV Registry
IANA is requested to create sub-registry in MPLS RTM TLV Registry,
requested in Section 8.2, called "MPLS RTM Sub-TLV Registry". All
code points in the range 0 through 127 in this registry shall be
allocated according to the "IETF Review" procedure as specified in
[RFC5226] . Remaining code points are allocated according to the
table below. This document defines the following new values RTM sub-
TLV types:
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+-----------+-------------+-------------------------+
| Value | Description | Reference |
+-----------+-------------+-------------------------+
| 0 | Reserved | This document |
| 1 | PTP 2-step | This document |
| 2-127 | Reserved | IETF Consensus |
| 128 - 191 | Reserved | First Come First Served |
| 192 - 255 | Reserved | Private Use |
+-----------+-------------+-------------------------+
Table 3: RTM Sub-TLV Type
8.4. RTM Capability sub-TLV
IANA is requested to assign a new type for RTM Capability sub-TLV
from future OSPF Extended Link TLV Sub-TLVs registry as follows:
+-------+----------------+---------------+
| Value | Description | Reference |
+-------+----------------+---------------+
| TBA2 | RTM Capability | This document |
+-------+----------------+---------------+
Table 4: RTM Capability sub-TLV
8.5. IS-IS RTM Application ID
IANA is requested to assign a new Application ID for RTM from the
Application Identifiers for TLV 251 registry as follows:
+-------+-------------+---------------+
| Value | Description | Reference |
+-------+-------------+---------------+
| TBA3 | RTM | This document |
+-------+-------------+---------------+
Table 5: IS-IS RTM Application ID
8.6. RTM_SET Object RSVP Class Number, Class Type and Sub-object Types
IANA is requested to assign a new Class Number for RTM_SET object as
follows:
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+-------+----------------+---------------+
| Value | Description | Reference |
+-------+----------------+---------------+
| TBA4 | RTM_SET object | This document |
+-------+----------------+---------------+
Table 6: RTM_SET object Class
IANA is requested to assign a new Class Type for RTM_SET object as
follows:
+-------+-------------+---------------+
| Value | Description | Reference |
+-------+-------------+---------------+
| TBA5 | RTM Set | This document |
+-------+-------------+---------------+
Table 7: RTM_SET object Class Type
IANA requested to create new sub-registry for sub-object types of
RTM_SET object as follows:
+-----------+----------------------+-------------------------+
| Value | Description | Reference |
+-----------+----------------------+-------------------------+
| 0 | Reserved | |
| 1 | IPv4 address | This document |
| 2 | IPv6 address | This document |
| 3 | Unnumbered interface | This document |
| 4-127 | Reserved | IETF Consensus |
| 128 - 191 | Reserved | First Come First Served |
| 192 - 255 | Reserved | Private Use |
+-----------+----------------------+-------------------------+
Table 8: RTM_SET object sub-object types
9. Security Considerations
Routers that support Residence Time Measurement are subject to the
same security considerations as defined in [RFC5586] .
In addition - particularly as applied to use related to PTP - there
is a presumed trust model that depends on the existence of a trusted
relationship of at least all PTP-aware nodes on the path traversed by
PTP messages. This is necessary as these nodes are expected to
correctly modify specific content of the data in PTP messages and
proper operation of the protocol depends on this ability.
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As a result, the content of the PTP-related data in RTM messages that
will be modified by intermediate nodes cannot be authenticated, and
the additional information that must be accessible for proper
operation of PTP 1-step and 2-step modes MUST be accessible to
intermediate nodes (i.e. - MUST NOT be encrypted in a manner that
makes this data inaccessible).
While it is possible for a supposed compromised LSR to intercept and
modify the G-ACh content, this is an issue that exists for LSRs in
general - for any and all data that may be carried over an LSP - and
is therefore the basis for an additional presumed trust model
associated with existing LSPs and LSRs.
The ability for potentially authenticating and/or encrypting RTM and
PTP data that is not needed by intermediate RTM/PTP-capable nodes is
for further study.
Security requirements of time protocols are provided in RFC 7384
[RFC7384].
10. Acknowledgements
Authors want to thank Loa Andersson for his thorough review and
thoghtful comments.
11. References
11.1. Normative References
[I-D.ietf-ospf-ospfv3-lsa-extend]
Lindem, A., Mirtorabi, S., Roy, A., and F. Baker, "OSPFv3
LSA Extendibility", draft-ietf-ospf-ospfv3-lsa-extend-06
(work in progress), February 2015.
[I-D.ietf-ospf-prefix-link-attr]
Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", draft-ietf-ospf-prefix-link-attr-04 (work
in progress), April 2015.
[IEEE.1588.2008]
"Standard for a Precision Clock Synchronization Protocol
for Networked Measurement and Control Systems", IEEE
Standard 1588, March 2008.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[RFC3477] Kompella, K. and Y. Rekhter, "Signalling Unnumbered Links
in Resource ReSerVation Protocol - Traffic Engineering
(RSVP-TE)", RFC 3477, January 2003.
[RFC4385] Bryant, S., Swallow, G., Martini, L., and D. McPherson,
"Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
Use over an MPLS PSN", RFC 4385, February 2006.
[RFC5085] Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
Connectivity Verification (VCCV): A Control Channel for
Pseudowires", RFC 5085, December 2007.
[RFC5586] Bocci, M., Vigoureux, M., and S. Bryant, "MPLS Generic
Associated Channel", RFC 5586, June 2009.
[RFC5905] Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, June 2010.
[RFC6423] Li, H., Martini, L., He, J., and F. Huang, "Using the
Generic Associated Channel Label for Pseudowire in the
MPLS Transport Profile (MPLS-TP)", RFC 6423, November
2011.
[RFC6823] Ginsberg, L., Previdi, S., and M. Shand, "Advertising
Generic Information in IS-IS", RFC 6823, December 2012.
11.2. Informative References
[RFC4202] Kompella, K. and Y. Rekhter, "Routing Extensions in
Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4202, October 2005.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC6374] Frost, D. and S. Bryant, "Packet Loss and Delay
Measurement for MPLS Networks", RFC 6374, September 2011.
[RFC7384] Mizrahi, T., "Security Requirements of Time Protocols in
Packet Switched Networks", RFC 7384, October 2014.
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Authors' Addresses
Greg Mirsky
Ericsson
Email: gregory.mirsky@ericsson.com
Stefano Ruffini
Ericsson
Email: stefano.ruffini@ericsson.com
Eric Gray
Ericsson
Email: eric.gray@ericsson.com
John Drake
Juniper Networks
Email: jdrake@juniper.net
Stewart Bryant
Cisco Systems
Email: stbryant@cisco.com
Alexander Vainshtein
ECI Telecom
Email: Alexander.Vainshtein@ecitele.com
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